Entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and H. megidis) and entomopathogenic fungi (EPF) (Metarhizium anisopliae and Beauveria bassiana) were evaluated for efficacy against masked chafer white grub, Cyclocephala spp., under laboratory and greenhouse conditions, as well as their efficacy against various grub stages in the field.  Under both laboratory and greenhouse conditions, additive interactions were found between EPN and EPF in their combined application against Cyclocephala spp., except a few observations that showed antagonism or synergism.  Significantly greater control occurred from the combination of a nematode and a fungus compared with a fungus alone, but not compared with a nematode alone.  The combined effect did not differ significantly for nematode and fungi applied simultaneously or at different times.  EPF had no significant impact on EPN infection and production of infective juveniles (IJs) in grub carcasses.  Nematodes alone or in combination with fungi were comparable to the insecticide Merit 75 WP (imidacloprid) against 3rd instar Cyclocephala spp in the greenhouse. Efficacy of EPF and EPN varied dramatically between field sites and conditions; EPN and EPF applied alone or in combination were less effective than Merit 75 WP in >50% field trials, but some EPN + EPF treatments were more effective than the insecticide in reducing grub numbers.  EPN and EPF showed better potential than insecticides for providing extended control of white grubs in the subsequent generation.  In addition, the sub-lethal effects of EPF on southern masked chafer, C. lurida, were investigated.  Neither M. anisopliae nor B. bassiana had a sub-lethal effect on grub weight gain, adult longevity, oviposition, pupation and eclosion.  Finally, interaction between H. bacteriophora and M. anisopliae was examined to determine the potential of the nematode in improving fungal distribution in soil.  H. bacteriophora enhanced fungal distribution in sandy loam soil without grass thatch, but not in sandy soil with thatch.  In both soil types, soil depths significantly affected nematode and fungal distribution. In water profile, M. anisopliae conidia germinated hyphae that attached to sheath of H. bacteriophora IJs, which molted to detach from the fungus.  IJs mortality and virulence were not affected by the presence of M. anisopliae. / Ph. D.

White grubs (Coleoptera: Scarabaeidae) are important turfgrass pests in Virginia. Insecticides such as the neonicotinoid imidacloprid are commonly applied to turfgrass in order to control these pests. As an alternative to synthetic insecticides, entomopathogenic fungi (EPF), including Metarhizium brunneum (Petch) and Beauveria bassiana (Balsamo) Vuillemin may also be used for white grub control. The interaction of combining these two control tactics for white grubs in Virginia merits further investigation as does their effects on other soil organisms such as earthworms, which cohabitate with white grubs in turfgrass soil ecosystems. Herein, I investigate the following: 1) the efficacy of combined applications of the EPF, M. brunneum and B. bassiana with lower rates of imidacloprid or the diamide insecticide, chlorantraniliprole against white grubs; 2) interactions of earthworms with white grubs and EPF; and 3) the effect of white grub control products on earthworms. In the laboratory, a combined application of one half the recommended rate of chlorantraniliprole plus the full recommended rate of B. bassiana caused significantly higher mortality of third instar Cyclocephala spp. grubs than the untreated control. In the field, imidacloprid applied at lower rates as a single treatment or as part of a combined treatment with EPF resulted in significantly fewer grubs when applications were made in June. In the greenhouse, Japanese beetle, Popillia japonica Newman females laid a significantly reduced number of eggs in turf treated with lower rate of imidacloprid either applied as a single treatment or as part of a combined treatment compared with untreated control. In an earthworm-white grub interaction study, the earthworms Eisenia fetida (Savingy) and E. hortenis (Michaelsen) were shown to transfer B. bassiana spores from fungus-infected soil to uninfected soil in the laboratory. However, the presence of earthworms in fungal infected soil did not enhance the mortality of Cyclocephala spp. grubs. In bioassays conducted in the laboratory, only two neonicotinoids, dinotefuran and imidacloprid, caused significantly higher mortality to adult Lumbricus terrestris L. earthworms than untreated control consistently. When applied as a drench to turfgrass in spring, summer, and fall, none of the insecticides significantly reduced the earthworm densities compared with a water control. / Ph. D.